arXiv subjects

Zhen-Yang Wang

Publications and source records attributed to Zhen-Yang Wang.

30 records · Page 2Linked to original sources

arXiv2019

Studying the localized $CP$ violation and the branching fraction of the $\bar{B}^0\rightarrow K^-π^+π^+π^-$ decay

In this work, we study the localized $CP$ violation and the branching fraction of the four-body decay $\bar{B}^0\rightarrow K^-π^+π^-π^+$ by employing a quasi-two-body QCD factorization approach. Considering the interference of $\bar{B}^0\rightarrow \bar{K}_0^*(700)ρ^0(770)\rightarrow K^-π^+π^-π^+$ and $\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500)\rightarrow K^-π^+π^-π^+$ channels, we predict $\mathcal{A_{CP}}(\bar{B}^0\rightarrow K^-π^+π^-π^+)\in[0.15,0.28]$ and $\mathcal{B}(\bar{B}^0\rightarrow K^-π^+π^-π^+)\in[1.73,5.10]\times10^{-7}$, respectively, which shows that this two channels' interference mechanism can induce the localized $CP$ violation to this four-body decay. Meanwhile, within the two quark model framework for the scalar mesons $f_0(500)$ and $\bar{K}_0^*(700)$, we calculate the direct CP violations and branching fractions of the $\bar{B}^0\rightarrow \bar{K}_0^*(700)ρ^0(770)$ and $\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500)$ decays, respectively. The corresponding results are $\mathcal{A_{CP}}(\bar{B}^0\rightarrow \bar{K}_0^*(700)ρ^0(770)) \in [0.20, 0.36]$, $\mathcal{A_{CP}}(\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500))\in [0.08, 0.12]$, $\mathcal{B} (\bar{B}^0\rightarrow \bar{K}_0^*(700)ρ^0(770)\in [6.76, 18.93]\times10^{-8}$ and $\mathcal{B} (\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500))\in [2.66, 4.80]\times10^{-6}$, respectively, indicating the $CP$ violations of these two two-body decays are both positive and the branching fractions are quite different. These studies provide a new way to investigate the aforementioned four-body decay and could be helpful in clarifying the configuration of the structure of light scalar meson.

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arXiv2019

Rare $Λ_b \rightarrow Λl^+ l^- $ decay in the Bethe-Salpeter equation approach

We study the rare decays $Λ_b \rightarrow Λl^+ l^-~(l=e,μ, τ)$ in the Bethe-Salpeter equation approach. We find that depending on the values of parameters in our model the branching ratio $Br(Λ_b \rightarrow Λμ^+ μ^-)\times 10^{6}$ varies from $0.812$ to $1.445$ when $κ= 0.050 \sim 0.060$ GeV$^3$ and the binding energy $E_0=-0.14$ GeV while $Br(Λ_b \rightarrow Λμ^+ μ^-)\times 10^{6}$ varies from $1.051$ to $1.098$ when $κ= 0.055$ Gev$^3$ and the binding energy $E_0$ changes from $-0.19$ to $-0.09$ GeV. These results agree with the experimental data. In the same parameter regions, we find that the branching ratio $Br(Λ_b \rightarrow Λe^+ e^-(τ^+ τ^-) )\times 10^{6}$ varies in the range $0.660-1.028$ ($0.252-0.392$) and $0.749-1.098$ ($0.286-0.489$), respectively.

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arXiv2019

Study of localized $CP$ violation in $B^-\rightarrow π^- π^+π^-$ and the branching ratio of $B^-\rightarrow σ(600)π^-$ in the QCD factorization approach

In this work, within the QCD factorization approach, we study the localized integrated $CP$ violation in the $B^-\rightarrow π^-π^+π^-$ decay and the branching fraction of the $B^-\rightarrowσπ^-$ decay. Both the resonance and nonresonance contributions are included when we study the localized $CP$ asymmetry in the $B^-\rightarrow π^-π^+π^-$ decay. The resonance contributions from the scalar $σ(600)$ and vector $ρ^0(770)$ mesons are included. For the $σ(600)$ meson, we apply both the Breit-Wigner and Bugg models to deal with its propagator, and obtain $\mathcal{B}(B^-\rightarrow σ(600)π^-)<1.67\times10^{-6}$ and $\mathcal{B}(B^-\rightarrow σ(600) π^-)<1.946\times10^{-5}$ in these two models, respectively. We find that there is no allowed divergence parameters $ρ_S$ and $ϕ_S$ to satisfy the experimental data $\mathcal{A_{CP}}(π^-π^+π^-)=0.584\pm0.082\pm0.027\pm0.007$ in the region $m_{π^+π^- \mathrm{high}}^2>15$ $\mathrm{GeV}^2$ and $m_{π^+π^-\mathrm{low}}^2<0.4$ $\mathrm{GeV}^2$ and the upper limit of $\mathcal{B}(B^-\rightarrow σ(600)π^-)$ in the Breit-Wigner model, however, there exists the region $ρ_S\in[1.70,3.34]$ and $ϕ_S \in [0.50,4.50]$ satisfying the data for $\mathcal{A_{CP}}(π^-π^+π^-)$ and the upper limit of $\mathcal{B}(B^-\rightarrow σ(600)π^-)$ in the Bugg model. This reveals that the Bugg model is more plausible than the Breit-Wigner model to describe the propagator of the $σ(600)$ meson even though the finite width effects are considered in both models. The large values of $ρ_S$ indicate that the contributions from weak annihilation and hard spectator scattering processes are both large, especially, the weak annihilation contribution should not be negleted for $B$ decays to final states including a scalar meson.

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arXiv2019

$B_{s1}(5778)$ as a $B^*\bar{K}$ molecule in the Bethe-Salpeter equation approach

We interpret the $B_{s1}(5778)$ as an $S$-wave $B^\ast\bar{K}$ molecular state in the Bethe-Salpeter equation approach. In the ladder and instantaneous approximations, and with the kernel containing one-particle-exchange diagrams and introducing three different form factors (monopole, dipole, and exponential form factors) in the vertex, we find the bound state exists. We also study the decay widths of the decay $B_{s1}(5778)\rightarrow B_s^\astπ$ and the radiative decays $B_{s1}(5778)\rightarrow B_sγ$ and $B_{s1}(5778)\rightarrow B_s^{\ast}γ$, which will be instructive for the forthcoming experiments.

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arXiv2019

Studying the bound state of the $B\bar{K}$ system in the Bethe-Salpeter formalism

In this work, we study the $B\bar{K}$ molecule in the Bethe-Salpeter (BS) equation approach. With the kernel containing one-particle-exchange diagrams and introducing two different form factors (monopole form factor and dipole form factor) in the vertex, we solve the BS equation numerically in the covariant instantaneous approximation. We investigate the isoscalar and isovector $B\bar{K}$ systems, and we find $X(5568)$ cannot be a $B\bar{K}$ molecule.

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arXiv2019

Analyzing $Ξ(1620)$ in the molecule picture in the Bethe-Salpeter equation approach

In this work, we assume that the observed state $Ξ(1620)$ is a $s$-wave $Λ\bar{K}$ or $Σ\bar{K}$ bound state. Based on this molecule picture, we establish the Bethe-Salpeter equations for $Ξ(1620)$ in the ladder and instantaneous approximations. We solve the Bethe-Salpeter equations for the $Λ\bar{K}$ and $Σ\bar{K}$ systems numerically and find that the $Ξ(1620)$ can be explained as $Λ\bar{K}$ and $Σ\bar{K}$ bound states with $J^P=1/2^-$, respectively. Then we calculate the decay widths of $Ξ(1620)\rightarrowΞπ$ in these two different molecule pictures systems, respectively.

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arXiv2018

Study of $CP$ Violation in $B^-\rightarrow K^- π^+π^-$ and $B^-\rightarrow K^- σ(600)$ decays in the QCD factorization approach

In this work, we study the localized $CP$ violation in $B^-\rightarrow K^-π^+π^-$ and $B^-\rightarrow K^- σ(600)$ decays by employing the quasi two-body QCD factorization approach. Both the resonance and the nonresonance contributions are studied for the $B^-\rightarrow K^-π^+π^-$ decay. The resonance contributions include those not only from $[ππ]$ channels including $σ(600)$, $ρ^0(770)$ and $ω(782)$ but also from $[Kπ]$ channels including $K^*(892)$, $K_0^*(1430)$, $K^*(1410)$, $K^*(1680)$ and $K_2^*(1430)$. By fitting the experimental data $\mathcal{A_{CP}}(K^-π^+π^-)=0.678\pm0.078\pm0.0323\pm0.007$ for $m_{K^-π^+}^2<15$ $\mathrm{GeV}^2$ and $0.08<m_{π^+π^-}^2<0.66$ $\mathrm{GeV}^2$, we get the end-point divergence parameters in our model, $ϕ_S \in [4.75, 5.95]$ and $ρ_S\in[4.2, 8]$. Using these results for $ρ_S$ and $ϕ_S$, we predict that the $CP$ asymmetry parameter $\mathcal{A_{CP}} \in [-0.094, -0.034]$ and the branching fraction $\mathcal{B} \in [1.82, 20.0]\times10^{-5}$ for the $B^-\rightarrow K^-σ(600)$ decay. In addition, we also analyse contributions to the localized $CP$ asymmetry $\mathcal{A_{CP}}(B^-\rightarrow K^-π^+π^-)$ from $[ππ]$, $[Kπ]$ channel resonances and nonresonance individually, which are found to be $\mathcal{A_{CP}}(B^-\rightarrow K^-[π^+π^-] \rightarrow K^-π^+π^-)=0.585\pm0.045$, $\mathcal{A_{CP}}(B^-\rightarrow [K^-π^+] π\rightarrow K^-π^+π^-)=0.086\pm0.021$ and $\mathcal{A_{CP}}^{NR}(B^-\rightarrow K^-π^+π^-)=0.061\pm0.0042$, respectively. Comparing these results, we can see that the localized $CP$ asymmetry in the $B^-\rightarrow K^-π^+π^-$ decay is mainly induced by the $[ππ]$ channel resonances while contributions from the $[Kπ]$ channel resonances and nonresonance are both very small.

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arXiv2018

Residues of $Λ_Q$-type and $Σ_Q$-type Baryons in the Bethe-Salpeter Equation Approach

We study the residues of $Λ_Q$-type baryons ($Λ_Q$ and $Ξ_Q^A$) $(Q=b,c)$ and $Σ_Q$-type baryons ($Σ_Q^{(\ast)}$, $Ξ_Q^{S(\ast)}$ and $Ω_Q^{(\ast)}$) in the quark-diquark model within the Bethe-Salpeter (BS) formalism. These residues can be used, for example, in the calculations of the amplitudes in the scattering processes. After constructing the baryonic currents in the BS formalism, we derive the relations between the BS wave functions and the residues for these baryons. The BS equations are solved numerically with the kernel including the scalar confinement and the one gluon exchange terms and with the covariant instantaneous approximation being employed in the calculations. Finally, we obtain the numerical values of the residues $0.103\,\rm GeV\sim0.224\,\rm GeV$ for $Λ_Q$, $0.143\,\rm GeV\sim0.215\,\rm GeV$ for $Ξ_Q^A$, $0.262\,\rm GeV\sim0.361\,\rm GeV$ for $Σ_Q^{(\ast)}$, $0.313\,\rm GeV\sim0.460\,\rm GeV$ for $Ξ_Q^{S(\ast)}$ and $0.473\,\rm GeV\sim0.571\,\rm GeV$ for $Ω_Q^{(\ast)}$ in the ranges of the parameters in our model.

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arXiv2018

Study of $CP$ Violations in $B^-\rightarrow K^- π^+π^-$ and $B^-\rightarrow K^- f_0(500)$ decays in the QCD factorization approach

Within the QCD factorization approach, we study the $CP$ violations in $B^-\rightarrow K^-π^+π^-$ and $B^-\rightarrow K^- f_0(500)$ decays. We find the experimental data of the localized $CP$ asymmetry in $B^-\rightarrow K^-π^+π^-$ decays in the region $m_{K^-π^+}^2<15$ $\mathrm{GeV}^2$ and $0.08<m_{π^+π^-}^2<0.66$ $\mathrm{GeV}^2$ can be explained by the interference of two intermediate resonances, $ρ^0(770)$ and $f_0(500)$ when the parameters in our interference model are in the allowed ranges, i.e. the relative strong phase $δ\in[0, 1.745]\cup[3.578, 6.266]$ and the end-point divergence parameters $ρ_S\in[2.790, 5.290]$ and $ϕ_S \in [1.518, 5.183]$. With the obtained allowed ranges for $ρ_S$ and $ϕ_S$, we obtain the predictions for the $CP$ asymmetry parameter $A_{CP} \in [-0.259, 0.006]$ and the branching fraction $\mathcal{B} \in [0.585, 3.230]\times10^{-5}$ for $B^-\rightarrow K^-f_0(500)$ decay modes.

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arXiv2017

X(3872) as a molecular $D\bar{D}^*$ state in the Bethe-Salpeter equation approach

We discuss the possibility that the X(3872) can be a $D\bar{D}^*$ molecular bound state in the Bethe-Salpeter equation approach in the ladder and instantaneous approximations. We show that the $D\bar{D}^*$ bound state with quantum numbers $J^{PC}=1^{++}$ exists. We also calculate the decay width of $X(3872) \rightarrow γJ/ψ$ channel and compare our result with those from previous calculations.

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arXiv2017

Spectra of charmed and bottom baryons with hyperfine interaction

Up to now, the excited charmed and bottom baryon states are still not well studied both experimentally and theoretically. In the present paper, we predict the mass of $Ω_b^*$, the only $L = 0$ baryon state which has not been observed, to be 6069.2 MeV. The spectra of charmed and bottom baryons with the orbital angular momentum $L = 1$ are studied in two popular constituent quark models, the Goldstone boson exchange (GBE) and the one gluon exchange (OGE) hyperfine interaction models, respectively. Inserting the latest experimental data from the "Review of Particle Physics", we find that in the GBE model, there exist some multiplets ($Σ_{c(b)}$, $Ξ'_{c(b)}$ and $Ω_{c(b)}$) which total spins of three quarks in their lowest energy states are 3/2, but in the OGE model there is no such phenomenon. This is the most important difference between the GBE and OGE models. These results can be tested in the near future. We suggest more efforts to study the excited charmed and bottom baryons both theoretically and experimentally, not only for the abundance of baryon spectra, but also for determining which hyperfine interaction model is realized in nature.

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arXiv2015

Localized direct CP violation in $B^\pm\rightarrow ρ^0 (ω)π^\pm\rightarrow π^+ π^-π^\pm$

We study the localized direct CP violation in the hadronic decays $B^\pm\rightarrow ρ^0 (ω)π^\pm\rightarrowπ^+ π^-π^\pm$, including the effect caused by an interesting mechanism involving the charge symmetry violating mixing between $ρ^0$ and $ω$. We calculate the localized integrated direct CP violation when the low invariant mass of $π^+π^-$ [$m(π^+π^-)_{low}$] is near $ρ^0(770)$. For five models of form factors investigated, we find that the localized integrated direct CP violation varies from -0.0170 to -0.0860 in the ranges of parameters in our model when $0.750<m(π^+π^-)_{low}<0.800$\,GeV. This result, especially the sign, agrees with the experimental data and is independent of form factor models. The new experimental data shows that the signs of the localized integrated CP asymmetries in the regions $0.470<m(π^+π^-)_{low}<0.770$\,GeV and $0.770<m(π^+π^-)_{low}<0.920$\,GeV are positive and negative, respectively. We find that $ρ$-$ω$ mixing makes the localized integrated CP asymmetry move towards the negative direction, and therefore contributes to the sign change in those two regions. This behavior is also model independent. We also calculate the localized integrated direct CP violating asymmetries in the regions $0.470<m(π^+π^-)_{low}<0.770$\,GeV and $0.770<m(π^+π^-)_{low}<0.920$\,GeV and find that they agree with the experimental data in some models of form factors.

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